This invention relates to the art of perforating sheet material, and more particularly to a new and improved method and apparatus for providing closely spaced small diameter holes in sheet material such as conveyor belts.
One area of use of the present invention is in micro-drilling a series of closely spaced holes in a conveyor belt to a facilitate passage of air through the belt thus providing suction and vacuum hold-down of items such as sheet material carried on the conveyor belt. By way of illustration, such conveyor belts in vacuum hold-down apparatus used in the cloth cutting industry have very dense hole patterns, i.e. nearly a million small diameter closely spaced holes in a belt six feet wide and fifty feet long. In addition to the ability to provide even smaller diameter holes in closer spaced relation, an important consideration is providing the holes in a manner that does not impart structural weakness in the belt.
It would, therefore, be highly desirable to provide a new and improved system and method for perforating sheet material such as conveyor belts which provides relatively smaller diameter holes in closer spaced relation and yet which avoids imparting significant structural weakness to the perforated sheet material.
The present invention provides a method and apparatus for perforating sheet material wherein the resulting perforations are in a predetermined pattern which avoids imparting structural weakness to the perforated sheet material. The predetermined pattern includes spaced perforations along linear paths which are spaced along one linear dimension of the sheet material and each of which paths is disposed at an acute angle relative to another linear dimension of the sheet material. The predetermined pattern avoids straight paths of perforations along the longer linear dimension of the sheet material and thereby avoids imparting structural weakness to the material. Preferably the predetermined pattern is a series of herringbone patterns along the longitudinal dimension of the sheet with the rows of herringbone patterns and peaks thereof extending laterally of the sheet material. The pattern is formed by moving the sheet material in a first direction and scanning the material in a second direction with a pulsed laser beam.